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Abstract:

Toner particles and a dry-powder electrophoretic display employing such
particles are disclosed herein. The toner particles adapted for a
dry-powder electrophoretic display comprise emulsion/aggregation
particles having a negative charge. At least a portion of the toner
particles include a surface coating, comprising a methacrylate polymer,
disposed on the surface of the toner particles to impart a positive
charge to a set of toner particles. The emulsion/aggregation toner
particles have a particle size generally less than about 10 micrometers
that allows for improved image quality as compared to conventional toners
utilized in dry-powder electrophoretic displays.

Claims:

1. A dry-powder electrophoretic display comprising:a pair of electrodes
disposed opposite one another;a spacer layer disposed between the
electrodes and defining an air gap therebetween;a first set of dry toner
particles comprising a plurality of toner particles of a first color and
a first charge; anda second set of dry toner particles comprising a
plurality of toner particles of a second color and a second
charge;wherein the toner particles of the second sets of dry toner
particles comprises a surface coating disposed on the surface of the
toner particles, said surface coating comprising a polymer selected from
the group of methacrylate polymers and polycarbonate polymers, and
imparting a positive charge to the toner particles.

2. The dry-powder electrophoretic display according to claim 1, wherein
said surface coating is a methacrylate polymer.

3. The dry-powder electrophoretic display according to claim 2, wherein
said methacrylate polymer is a copolymer of
butylmethacrylate-(2-dimethylaminoethyl)-methacrylate-methylmethacrylate.

4. The dry-powder electrophoretic display according to claim 3, wherein
the ratio of butylmethacrylate:(2-dimethylaminoethyl) methacrylate:
methylmethacrylate is about 1:2:1.

5. The dry-powder electrophoretic display according to claim 1, wherein
said surface coating is present in an amount of about 1 to about 10% by
weight of the toner particles upon which the coating is disposed.

6. The dry-powder eletrophoretic display according to claim 1, wherein
said surface coating is present in an amount of from about 3 to about 7%
by weight of the toner particles upon which the coating is disposed.

7. The dry-powder electrophoretic display according to claim 1, wherein
the toner particles comprising the surface coating have a particle size
from about 1 to about 20 microns.

8. The dry-powder electrophoretic display according to claim 3, wherein
the toner particles comprising the surface coating have a particle size
of from about 1 to about 10 microns.

9. The dry-powder electrophoretic display according to claim 3, wherein
the toner particles comprising the surface coating have a particle size
of from about 4 to about 7 microns.

10. A dry-powder electrophoretic display comprising:a cell having a viewed
region and a non-viewed region,a plurality of first toner particles
having a first electrical charge, said first toner particles comprising a
resin and a colorant; anda plurality of second toner particles having a
second electrical charge, said second toner particles comprising a resin,
a colorant and a surface coating disposed on the outer surface of the
particles;wherein said surface coating comprises a methacrylate polymer
and imparts a positive charge to the second toner.

11. The dry-powder electrophoretic display according to claim 10, wherein
said methacrylate polymer is a copolymer of
butylmethacrylate-(2-dimethylaminoethyl)-methacrylate-methylmethacrylate.

12. The dry-powder electrophoretic display according to claim 11, wherein
the ratio of butyl methacrylate:(2-dimethylaminoethyl)methacrylate:
methylmethacrylate is about 1:2:1.

13. The dry-powder electrophoretic display according to claim 10, wherein
said surface coating is present in an amount of about 1 to about 10 by
weight of the toner particles upon which the coating is disposed.

14. The dry-powder eletrophoretic display according to claim 10, wherein
said surface coating is present in an amount of from about 3 to about 7%
by weight of the toner particles upon which the coating is disposed.

15. The dry-powder electrophoretic display according to claim 10, wherein
the toner particles comprising the surface coating have a particle size
from about 1 to about 20 microns.

16. The dry-powder electrophoretic display according to claim 11, wherein
the toner particles comprising the surface coating have a particle size
of from about 1 to about 10 microns.

17. The dry-powder electrophoretic display according to claim 11, wherein
the toner particles comprising the surface coating have a particle size
of from about 4 to about 7 microns.

18. A dry-powder electrophoretic display comprising:a first electrode;a
second electrode disposed opposite the first electrode;a spacer layer
disposed between the first and second electrodes, the space layer
creating an air gap between the first and second electrode;a first set of
toner particles disposed between the first and second electrodes, the
first set of toner particles comprising a resin and a colorant, and
having a negative charge; anda second set of toner particles disposed
between the first and second electrodes, the second set of toner
particles comprising a resin and a colorant, and having a positive
charge, wherein the positive charge is produced by the application to the
second set of toner particles, a surface coating, in an amount of from
about 1 to about 10 percent by weight of the toner particles, formed from
a methacrylate polymer comprising a copolymer of
butylmethacrylate/(2-dimethylaminoethyl)methacrylate/methylmethacrylate.

19. The dry-powder electrophoretic display according to claim 18, wherein
the toner particles of each of the first and second sets of toner
particles have a particle size of from about 1 to about 20 microns.

20. The dry-powder electrophoretic display according to claim 18, wherein
the toner particles of each of the first and second sets of toner
particles have a particle size of about 10 microns or less.

21. The dry-powder electrophoretic display according to claim 18, wherein
the surface coating is present in an amount of from about 3 to about 7
percent by weight of the toner particles.

22. The dry-powder electrophoretic display according to claim 18, wherein
the ratio of buylmethacrylate to (2-dimethylaminoethyl)methacrylate to
methylmethacrylate is about 1:2:1.

23. A process for preparing a dry toner composition for use in a
dry-powder electrophoretic display, the process comprising:forming a
first set of dry toner particles comprising a resin and a colorant by an
emulsion aggregation process, said first set of dry toner particles
having a negative charge; andforming a second set of dry toner particles
comprising a resin latex and a colorant, the second set of dry toner
particles being formed by heating a mixture of a latex and a colorant at
a temperature of below about the glass transition temperature (Tg) of a
polymer contained in the latex; and cooling the mixture;wherein said
second set of dry toner particles is further wet surface treated with a
methacrylate polymer by adding a methacrylate polymer solution to the
mixture of the latex and colorant subsequent to the cooling of the latex
and colorant mixture, and adjusting the pH of the resulting solution to
above about 7 thereby permitting the methacrylate polymer to precipitate
on the toner particles, said methacrylate polymer providing a positive
charge to the surface of the toner particles of the second set of dry
toner particles.

24. A process in accordance with claim 23, wherein said methacrylate
polymer is a
butylmethacrylate-(2-dimethylaminoethyl)methacrylate-methylmethacrylate
copolymer (1:2:1) comprising (2-dimethylaminoethyl) methacrylate, butyl
methacrylate and methyl methacrylate, the methacrylate polymer having a
mean molecular weight, Mw, of from about 125,000 to about 175,000.

25. A process in accordance with claim 23, wherein said methacrylate
polymer is present in an amount of from about 1 to about 10 weight
percent.

26. A process in accordance with claim 23, wherein said methacrylate
polymer is present in an amount of from about 3 to about 7 weight
percent.

27. A process in accordance with claim 23, wherein said methacrylate
polymer is a
butylmethacrylate-(dimethylaminoethyl)methacrylate/methylmethacrylate
copolymer present in an amount of from about 1 to about 10 weight
percent.

28. A process in accordance with claim 23, wherein said methacrylate
polymer is a
butylmethacrylate-(dimethylaminoethyl)methacrylate/methylmethacrylate
copolymer present in an amount of from about 3 to about 7 weight percent.

29. A process in accordance with claim 23, wherein said pH is from about 8
to about 12.

30. A process in accordance with claim 23, wherein said pH is from about
10 to about 11.

31. A process in accordance with claim 29, wherein the pH of the resulting
mixture after heating is from about 2 to about 5 and which pH is
increased to from about 9 to about 12 subsequent to the addition of said
methacrylate.

32. A process in accordance with claim 29, wherein the pH of the resulting
mixture after heating is from about 2 to about 4 and which pH is
increased to from about 10 to about 12 subsequent to the addition of said
methacrylate.

33. A process in accordance with claim 23, further comprising a second
heating at a temperature of about 70.degree. C. to about 95.degree. C.
and wherein coalescence results for said latex resin, said colorant and
said methacrylate, and which methacrylate is present on the surface of
said resulting toner.

Description:

[0001]This is a divisional of application of U.S. Ser. No. 10/973,544,
filed Oct. 26, 2004, entitled "Toner Compositions for Dry-Powder
Electrophoretic Displays", by Naveen Chopra et al., the disclosure of
which is hereby incorporated by reference in its entirety.

BACKGROUND

[0002]The present disclosure relates, in various exemplary embodiments, to
toner compositions and processes for producing the same. The present
disclosure also relates to dry-powder electrophoretic displays employing
such toner compositions.

[0003]Photo-electrophoretic imaging systems and electrophoretic displays
are known in the art. Electrophoretic imaging systems and displays
generally include electrically photosensitive pigment particles dispersed
in a carrier liquid, or suspending fluid, and arranged between two
parallel and generally transparent conducting electrode panels.

[0004]Conventional electrophoretic display systems are typically one of
two types, namely, a one particle system or a two particle system. In a
one particle system, the suspending fluid is colored with a dye. In a two
particle system, two types of particles of different colors and opposite
charge are dispersed in a clear fluid. Particles acquire their charge via
the adsorption of polymeric charge control agents (CCAs) that are added
to the fluid. Under the influence of an electric field, the charged
particles migrate towards the oppositely charged electrode.

[0005]The particles are typically prepared using a liquid toner process to
create composite particles consisting of a pigment and a resin. The
particles generally range from about 1 to about 10 micrometers in size.
The resin used includes thermoplastics such as a poly(ethylene-co-vinyl
acetate) or a poly(ethylene-co-methacrylic acid). The particles are then
encapsulated in a microcapsule or a photopolymer structure to produce a
display device.

[0006]Electrophoretic displays using these liquid systems, however, have a
number of drawbacks. In unencapsulated systems, for example, articles
that make up the system tend to cluster and settle, which reduces the
performance and the life of the electrophoretic display. Encapsulated
systems also experience performance problems over time. For example,
above 60° C., the polymer becomes soft and sticky, which leads to
particle agglomeration and overall degradation in device performance.
These problems limit the robustness of the materials packaging, and
preclude any device preparation steps, such as hot lamination.
Additionally, the desorption of charge control agents from the particles
in the solution leads to decay of the electrophoretic mobility of the
particles.

[0007]As an alternative to conventional electrophoretic displays utilizing
liquid systems, there is a growing interest in dry-powder electrophoretic
displays. Dry-powder electrophoretic displays as used herein refers to
electrophoretic displays wherein the toner particles are not dispersed in
a suspending fluid or encapsulated as is understood in the art. Dry-power
electrophoretic displays offer advantages over conventional liquid
electrophoretic systems. An important aspect is that the solventless
nature of the dry-powder display greatly reduces the loss of particle
charge over time. Additionally, known dry-powder electrophoretic displays
are typically limited by the size of the toner particles, i.e., up to
about 50 micrometers, employed in such systems. The use of large toner
particles, however, often results in poor image quality and visual
graininess.

[0008]It is therefore desirable to provide a new dry-powder
electrophoretic display system. It is further desirable to provide toner
compositions and particles suitable for use in such a system.

BRIEF DESCRIPTION

[0009]The present disclosure provides, in various exemplary embodiments, a
dry toner composition, and/or a dry-powder electrophoretic display
incorporating such a toner composition, that achieves one or more of the
foregoing.

[0010]In one aspect, a toner composition is provided comprising negatively
charged emulsion aggregation part ices and a colorant. A surface coating
comprising a polymer selected from methacrylate polymers or polycarbonate
polymers is disposed on a portion of the toner particles, wherein the
surface coating imparts a positive charge characteristic to the surface
of the particles. The negatively and positively charged dry toner
particles so produced are particularly beneficial for use in dry-powder
electronic displays.

[0011]In another aspect, the present disclosure provides a dry-powder
electrophoretic display comprising a pair of electrodes disposed opposite
one another and a spacer layer disposed between the electrodes to define
an air gap therebetween. Included in the air gap is a first dry toner
composition comprising a plurality of negatively charged toner particles
of a first color, and a second dry toner composition comprising a
plurality of toner particles of a different or second color and a
different or second charge. In this regard, the toner particles of the
second dry toner composition are covered with a surface coating to impact
a positive charge. The surface coating is comprised of a polymer selected
from methacrylate polymers or polycarbonate polymers. The first and
second dry toner compositions are included in the air gap to produce a
dry-powder electrophoretic display.

[0012]In still another aspect, the present disclosure provides a
dry-powder electrophoretic display that comprises a cell having a viewed
region and a non-viewed region. The cell contains a plurality of first
toner particles comprising a resin and a colorant and having a negative
charge, and a plurality of second toner particles comprising a resin and
a second colorant. The colorants of the first toner particles and the
second toner particles differ from one another. A surface coating is
disposed on the outer surface of the second toner particles, wherein the
surface coating comprises a methacrylate polymer and imparts a positive
charge.

[0013]In yet another aspect, the present disclosure provides a dry-powder
electrophoretic display that comprises a first electrode, a second
electrode disposed opposite the first electrode, a spacer layer disposed
between the first and second electrodes and creating an air gap
therebetween, a first set of toner particles disposed between the first
and second electrodes, and a second set of toner particles disposed
between the first and second electrodes. The first set of toner particles
comprises a resin and a colorant, and has a negative charge. The second
set of toner particles comprises a resin and a colorant and further
comprises a surface coating in an amount of about 1 to about 10 percent
by weight of the toner particles to impact a positive charge. A
non-limiting example of such a surface coating is a methacrylate polymer
comprising a copolymer of
butylmethacrylate/(2-dimethylaminoethyl)methacrylate methylmethacrylate.

[0014]In a further aspect, the present disclosure provides a process for
preparing a dry toner composition for use in a dry-powder electrophoretic
display. The process comprises forming a first set of dry toner particles
comprising a resin and a colorant by an emulsion aggregation process,
said first set of dry toner particles having a negative charge; and
forming a second set of dry toner particles comprising a resin latex and
a colorant and an outer coating, said second set of dry toner particles
having a positive charge. Optionally, the second set of dry toner
particles may be formed by heating a mixture of a latex and a colorant at
a temperature of below about the glass transition temperature (Tg) of a
polymer contained in the latex; and cooling the mixture; wherein said
second set of dry toner particles is further wet surface treated with a
methacrylate polymer by adding a methacrylate polymer solution to the
mixture of the latex and colorant subsequent to the cooling of the latex
and colorant mixture, and adjusting the pH of the resulting solution to
above about 7 thereby permitting the methacrylate polymer to precipitate
on the toner particles, said methacrylate polymer providing a positive
charge to the surface of the toner particles of the second set of dry
toner particles.

[0015]These and other aspects of the disclosure are more particularly
discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]The following is a brief description of the drawings, which are
presented for the purposes of illustrating the disclosure described
herein and not for the purposes of limiting the same.

[0017]FIG. 1 is a schematic cross-section of an electrophoretic display in
accordance with one exemplary embodiment;

[0018]FIG. 2 depicts a series of cells containing toner particles in an
air gap of a dry-powder electrophoretic display; and

[0019]FIG. 3 shows a top perspective of a sample portion of several cells
arranged in a grid or array.

DETAILED DESCRIPTION

[0020]The present disclosure, as illustrated in various exemplary
embodiments, relates to dry-powder electrophoretic displays employing
toner particles comprising emulsion/aggregation particles. Generally, the
dry-powder electrophoretic displays include at least two sets of toner
particles, wherein the color of one set of toner particles differs from
the color of the other sets of toner particles. Additionally, one set of
toner particles has a charge opposite the charge of the other set of
toner particles. That is, one set of toner particles carries a negative
charge, while the other set of toner particles carries a positive charge.
For example, one set of toner particles in the display includes
negatively charged emulsion/aggregation particles and the other set of
toner particles includes a surface coating to impart a positive charge to
the surface of the toner particles. The negatively and positively charged
dry toner compositions so produced are particularly beneficial for use in
dry-powder electronic displays.

[0021]The present electrophoretic displays may have any configuration
suitable for use in a dry-powder electrophoretic display. Generally the
electrophoretic display includes a pair of electrodes disposed opposite
one another, an air gap between the electrodes, and two sets of toner
particles of different colors and opposite charges disposed within the
air gap and between the electrodes. In embodiment, the electrodes are
substantially planar, and the opposing electrodes are substantially
parallel to one another. The air gap is substantially free of any
dispersions or suspending fluids that are typically present as in
conventional electrophoretic displays. As used herein, the term "air gap"
refers to a gap between the electrodes that comprises air or other
suitable gas such as, for example, argon. The dry-powder electrophoretic
display substantially free of a suspending liquid as is understood in the
art.

[0022]With reference to FIG. 1, an electrophoretic display 10 includes a
pair of opposing, substantially parallel electrodes 12a and 12b. Two or
more spacer beads 14 are disposed between the electrodes 12a and 12b to
separate the electrodes and provide an air gap 16 between the inner
surfaces of the electrodes. Disposed between the electrodes are a so a
plurality of toner particles 18 and 20.

[0023]The toner particles 18 and 20 are oppositely charged toner
compositions, That is, one of toner particles 18 and 20 is negatively
charged, and one of toner particles 18 and 20 is positively charged.
Additionally, the toner particles 18 have a different color from the
toner particles 20. There is no dispersion fluid between the electrode
substrate, i.e., within the air gap 16. As the charge of the electrodes
12a and 12b is reversed, the oppositely charged toner particles migrate
across the air gap 16 in response to the electric field, creating a light
or dark image.

[0024]Referring to FIG. 2, a two-particle electrophoretic display 22 is
shown, which consists of one particle species of a first color 24 (e.g.
white) and another particle species of a second color 26 (e.g. black). An
optically transmissive cell 28 surrounds the particles which are
dispersed in an air gap 30 between the electrodes and substrates. Cells,
such as cells 28, are used to prevent particle setting and particle
agglomeration. The first and second particles 24, 26 differ from each
other optically and in terms of at least one other physical
characteristic that provides the basis for their separation. For example,
the particles 24, 26 are colored differently and have different surface
charges. As shown, the two-particle system consists of one particle
species of a first white color 24 and another particle species of a
second color 26, e.g., black, cyan, magenta, yellow, blue, red, or the
like. In one configuration, the colored particles 26 carry a positive
charge, while the white colored particles 24 carry a negative charge. The
particle size can range from about 0.1 micron to about 20 microns. In the
absence of an electric field, the particles 24, 26 are substantially
immobile. Further, in the absence of an electric field, the particles 24,
26 may be attracted to the surfaces by Van der Waals forces or
electrostatic forces.

[0025]As shown in FIG. 2, three cells 28 are displayed. It will be
appreciated that any number of grids or arrays 32 of cells 28 may be
arranged (refer to FIG. 3). It is further appreciated that the actual
display of a colored state 34 or a white color state 36 is accomplished
by manipulating the position of the particles 24, 26 in each cell 28 in
correspondence with the observing angle 38. As shown, the cells 28 are
cubical in geometry. It will be further appreciated that any number of
geometric configurations may be utilized. The cells 28 represent a spacer
layer and may be made from a photopolymer (i.e. SU-8 distributed by
Microchem Corp.). The cells may also be made by molding or embossing. The
walls 38 of the cells 28 may be coated with a material that provides a
desired surface energy to prevent excessive particle adhesion. Some level
of particle adhesion is acceptable, and even desirable if bistability of
the display is required. The adhesion forces, however should be low
enough so that particles can be removed from the surfaces, with a
relatively low electric field For the electrophoretic displays described
herein, the cell geometry is not essential. As an example, the visible
square viewing region 40, as shown in FIG. 3, is approximately 200
microns along each side. The use of separate cells 28 prevents
agglomeration and settling of the particles 24, 26.

[0026]Referring again to FIG. 2, an addressing scheme for controlling the
color state of the display 22 is shown in which an electrode 42 (or set
of electrodes) is adjacent a non-viewed region 44 (i.e. bottom or rear
surface or back-plane) of the cells 28 and another continuous top
electrode 46 is adjacent a viewed region 47 (i.e. top or front surface,
or front-plane) of the cells 28. The top electrode 46 may take the form
of an indium tin oxide coating (ITO) of a transparent glass substrate 48
overlying the cell array 32. The glass substrate 48 may be similar to
those used in liquid crystal displays. The ITO top electrode 46 may be
evaporated onto the top glass substrate 48. The ITO top electrode 46 is
transparent, and the colored states 34, 36 are viewed through the ITO top
electrode 46.

[0027]Underlying the cell array 32 is a glass bottom substrate 50. It will
be appreciated that any addressing scheme may be used in an
electrophoretic display in accordance with the present disclosure
including, but not limited to, a direct addressing scheme having a fixed
electrode pattern, an active matrix addressing scheme with a pixilated
electrode array, and a passive matrix addressing scheme with a top and
bottom plate patterned in conductive stripes. For example, the bottom
substrate 50 may be a silicon wafer or a printed circuit board (PCB) with
patterned electrodes or an active matrix backplane. It will be
appreciated that the top and bottom electrodes 42, 46 may also be formed
from flexible material, such as ITO coated Mylar®. Mylar® is a
registered trademark of E.I. DuPont Corporation, Wilmington, Del.

[0028]It will also be appreciated that the viewed and the non-viewed
regions can be arranged laterally (not shown) so that the non-viewed
region (although observable) is significantly smaller in area with
respect to the viewed region (such as in laterally driven electrophoretic
displays).

[0029]The electrodes of the electrophoretic display device may be any
material suitable for such devices. At least one of the electrodes, and
in particular at least the top or upper electrode through which the
images formed by the device must be viewed, should be transparent in
order to enable such viewing. The bottom or back electrode does not have
to be transparent but may be, for example, a light reflecting or light
absorbing material. Suitable materials for the include but are not
limited to glass substrates, conductive plastic films and the like. For
example, the electrode may be plastic films coated with indium tin oxide
(ITO) such as polyethelyne terephthalate (PET) films, conductive glass
films, such as ITO coated glass film, and conductive thin metals. For
transparency, ITO coated plastic and glass films are typically used. The
electrodes or conductive substrates may be coated with an insulating
polymer or a polymer with a particular surface energy, tailored to meet a
use's particular needs, to provide the appropriate or desired amount of
particle adhesion.

[0030]The spacers may be any suitable material for a spacer and
electrophoretic display, and may be shaped in any suitable spacer design.
In embodiments, the spacer is made from fiber materials.

[0031]The spacers separate the electrodes and provide an air gap between
the electrodes in which the toner particles are allowed to move or
migrate. The spacers are sized to provide an acceptable air gap to allow
the electrophoretic device to properly function. The size of the air gap
depends on the voltage required to drive the particles back and forth
between the electrodes. The size of the air gap is also based on the
particle size of the toner. For operating at low voltages, the gap should
be as small as possible, but yet still allow multi-layer stacking of the
toner particles for good area coverage. Generally, the air gap should be
at least 3-10 times the diameter of the particles to allow for
satisfactory particle mobility and significant area coverage. In
embodiments, the air gap in the present dry-powder electrophoretic
devices is from about 3 to about 200 micrometers. In other embodiments,
the air gap is from about 20 to about 75 micrometers.

[0032]The toner particles are comprised of emulsion/aggregation particles,
and comprise a polymer or polymer mix, a colorant, and optionally a wax.
Emulsion/aggregation particles are particles prepared by
emulsion/aggregation processes. In emulsion/aggregation processes,
particles are achieved via aggregation as opposed to particle size
reduction. Emulsion/aggregation processes include the steps of emulsion,
aggregation, coalescence, washing, and drying. Emulsion/aggregation
processes for the preparation of toners are illustrated in a number of
Xerox patents, including U.S. Pat. No. 5,290,654; U.S. Pat. No.
5,278,020; U.S. Pat. No. 5,308,734; U.S. Pat. No. 5,370,963; U.S. Pat.
No. 5,344,738; U.S. Pat. No. 5,403,693; U.S. Pat. No. 5,418,180; U.S.
Pat. No. 5,364,729; and, U.S. Pat. No. 5,346,797, the disclosures of
which are incorporated in their entireties herein by reference.

[0033]The use of emulsion/aggregation particles as toner particles is
advantageous in that emulsion/aggregation particles have a very narrow
particle size distribution which provides more uniform movement of the
particles within the system, less likelihood of agglomeration problems
during operation of the electrophoretic display, and better display
quality.

[0034]The resin polymers used to form the toner particles are not limited
in any manner, and any material suitable for use in forming a toner
particle may be used. Generally, the emulsion/aggregation process is not
limited in the use of certain polymers. Examples of materials suitable to
form the toners include, but are not limited to, polyesters, polyamides,
polyimides, polyethelynes, polypropylenes, polyisobutyrates, acrylic
based polymers, such as styrene acrylate, and styrene methacrylate,
styrene butadiene, polyester-imide, ethylene-vinyl acetate copolymer, and
the like.

[0035]Suitable polyester resins include, but are not limited to, polyester
SPE2, available from Hercules Chemical, and polyesters of the formula:

##STR00001##

wherein Y is an alkali metal, X is a glycol, and n and m each represent
the number of segments.

[0037]Additionally, the polyester resin may be the resins described in
U.S. Pat. Nos. 6,593,049, and 6,756,176, the entire disclosures of which
are incorporated herein by reference. The toners may also comprise a
mixture of an amorphous polyester resin and a crystalline polyester resin
as described in copending U.S. Ser. No. 10/349,548, which is published as
U.S. Patent Application No. U.S. 2004/0142266, the entire disclosure of
which is incorporated herein by reference.

[0039]The toner particles may include any suitable colorant. Suitable
colorants include, but are not limited to dyes, pigments, and mixtures
thereof. The colorant is generally present in an amount of from about 1
to about 65% by weight of the toner. In embodiments, the colorant is
present in an amount of from about 2 to about 35% by weight of the toner,
and in other embodiments in an amount of from about 3 to about 15% by
weight of the toner. To form black toner particles, the colorant may be,
but is not limited to, carbon black, magnetites, surface treated
magnetites, and the like. White toner particles may be prepared by the
use of titanium dioxide, aluminum oxide, zirconium oxide, zinc dioxide,
and the like. Colored particles may be prepared by using colored pigments
or dyes, such as, for example, cyan, magenta, yellow, red, green, brown,
blue, or mixtures thereof.

[0041]Any suitable effective positive or negative charge enhancing
additive can be selected for the toner compositions of the present
disclosure. Such additives may be present in embodiments, in an amount of
about 0.1 to about 10, and, in other embodiments, may be present in an
amount of about 1 to about 3 percent by weight. Examples of these
additives include quaternary ammonium compounds inclusive of alkyl
pyridinium halides; alkyl pyridinium compounds, reference U.S. Pat. No.
4,298,672, the disclosure of which is totally incorporated hereby by
reference; organic sulfate and sulfonate compositions, reference U.S.
Pat. No. 4,338,390, the disclosure of which is totally incorporated
hereby by reference; cetyl pyridinium tetrafluoroborates; distearyl
dimethyl ammonium methyl sulfate; aluminum salts such as BONTRON E84®
or E88® (Hodogaya Chemical); and the like.

[0042]In embodiments, the process for forming the toner particles may
include (i) providing a coolant dispersion comprising a colorant, water,
an ionic surfactant, a nonionic surfactant or mixtures of a n ionic
surfactant and a nonionic surfactant, an providing a latex emulsion
comprising a resin, a nonionic surfactant and an ionic surfactant; (ii)
blending the colorant dispersion with the latex emulsion, resin, a
nonionic surfactant and an ionic surfactant and optionally adding a wax
dispersion comprised of, for example, submicron particles in the diameter
size range of from about 0.1 to about 0.4 micron dispersed in an ionic
surfactant of the same charge polarity as that of the ionic surfactant in
the colorant dispersion or latex emulsion; (iii) heating the resulting
mixture below about, or about equal to the glass transition temperature
(Tg) of the latex resin to form toner sized aggregates; and (iv)
heating the resulting aggregate suspension above about the Tg of the
latex resin. A surface coating as described herein, for example, a
methacrylate copolymer, available from Rohm American Inc. as
EUDRAGIT®, may be added to the above mixture and a toner which
contains a surface coating, such as the methacrylate copolymer, may be
isolated.

[0043]In other embodiments, the process may include (i) providing or
generating a latex emulsion of resin, water, and an ionic surfactant, and
providing or generating a colorant dispersion containing a colorant,
water, an ionic surfactant, or a nonionic surfactant; (ii) optionally
providing or generating a wax dispersion containing an anionic surfactant
similarly charged to that of the latex surfactant emulsion; (iii)
blending the wax dispersion (if used) with the colorant dispersion; (iv)
heating the resulting mixture below the glass transition temperature (Tg)
of the latex resin; (v) heating (iv) above about the Tg of the latex
resin; (vi) adding a surface coating as described herein, such as, for
example a methacrylate copolymer, available from Rohm American Inc. as
EUDRAGIT®, in an amount of from about 3 to about 7 weight percent;
(vii) retaining the mixture (vi) at a temperature of from about
70° C. to about 95° C. for about 3 to about 10 hours; (vii)
retaining the mixture (vi) at a temperature of from about 70° C.
to about 95° C. for about 3 to about 10 hours; (viii) washing the
resulting toner slurry; and (ix) isolating the toners.

[0044]The process may include adding an additional latex wherein the added
latex contains the same resin as the initial latex, or wherein the added
latex contains a dissimilar resin as compared to that of the initial
latex resin.

[0045]In embodiments, aggregation of the latex resin and colorant may be
accomplished by heating at a temperature below the glass transition
temperature of the resin or polymer contained in the latex and
coalescence may be accomplished by heating at a temperature of about the
glass transition temperature of the polymer contained in the latex to
enable fusion or coalescence of colorant and latex resin, followed by
mixing of the composition resulting with a surface coating solution, such
as a methacrylate copolymer. In embodiments, the aggregation temperature
may be from about 45° C. to about 55° C., and the
coalescence temperature may be from about 75° C. to about
97° C. In still other embodiments, the aggregation temperature is
from about 50° C. to about 60° C., and the coalescence
temperature is from about 80° C. to about 95° C.

[0046]In embodiments, the latex emulsion comprises submicron resin
particles in the size range of about 100 to about 500 nanometers, and
more specifically, in the size range of about 100 to about 500
nanometers, and more specifically, in the size range of about 150 to
about 400 nanometers in water and an ionic surfactant, and more
specifically, an anionic surfactant; the colorant dispersion comprises
submicron pigment particles of about 50 to about 250 nanometers and more
specifically, of about 80 to about 200 nanometers in size diameter; a
first coagulant comprising of a poly halide such as poly Aluminum
chloride (PAC) or poly aluminum sulfosilicate (PASS) and optionally a
second coagulant such as a cationic surfactant comprising, for example,
dialkyl benzenealkyl ammonium chloride, lauryl trimethyl ammonium
chloride, alkylbenzyl methyl ammonium chloride, alkyl benzyl dimethyl
ammonium bromide, benzalkonium chloride, cetyl pyridinium bromide,
C12, C15, C17 trimethyl ammonium bromides, halide salts of
quaternized polyoxyethylalkylamines, dodecylbenzyl triethyl ammonium
chloride, and which coagulant surfactant component is selected in an
amount of, for example, from about 0.01 to about 10 percent by weight of
toner; during or subsequent to heating, a second latex is added, and
which latex is comprised of submicron resin particles suspended in an
aqueous phase containing an ionic surfactant, and wherein the second
latex is optionally selected in an amount of about 15 to about 35 percent
by weight of the initial latex.

[0047]In other embodiments, the second latex is added and enables
formation of a coating on the resulting toner aggregates of (v), and
wherein the thickness of the formed coating is from about 0.1 to about 1
micron.

[0048]In embodiments, for example, white toner particles are prepared by
aggregating dispersions of a styrene butylacrylate, carboxylic acid
terpolymer, non cross-linked resin particles, a second cross-linked
copolymeric resin of styrene/butylacrylate/carboxylic acid divinyl
benzene, and a titanium dioxide pigment in the presence of two cationic
coagulants to provide aggregates. The aggregates have a particle size of
about 5.7 micrometers. The aggregates are then coalesced at temperatures
above the glass transition temperature of the non cross-linked resin to
provide spherical particles of 5.7 micrometers with a GSD of about 1.22.
Particles are then washed four times with dionized water and dried. Color
toners may be prepared in a similar manner, but with the use of a
different pigment to provide the appropriate or desired color.

[0049]In embodiments, toner particles, may be prepared by a process that
includes

[0050](i) blending a latex emulsion with a colorant dispersion comprised
of submicron, about for example 0.05 to about 1 micron in diameter,
particles suspended in a nonionic surfactant and water, and optionally
adding a wax dispersion comprised of submicron wax particles dispersed in
an ionic surfactant of a similar charge polarity to that of the ionic
surfactant in the latex emulsion, and wherein the latex contains
submicron resin particles, an ionic surfactant and water;

[0051](ii) adding to the blend two coagulants of a polymetal halide
dissolved in a strong acid and an ionic surfactant of opposite charge
polarity to that of the latex surfactant and pigment ionic surfactant to
initiate flocculation of the latex and the white particles;

[0052](iii) heating the resulting mixture below the glass transition
temperature (Tg) of the latex resin to form toner sized aggregates;

[0053](iv) optionally adding a latex to the formed toner aggregates;

[0054](v) adjusting the pH of the toner aggregates from about 1.8 to about
3 to a pH value of about 6.5 to about 8 with a base;

[0055](vi) heating the resulting aggregate suspension of (v) to above the
Tg of the latex resin;

[0056](vii) retaining the temperature of the mixture (vi) from about 70 to
about 95° C., followed by a reduction of the pH to about 4.8 to
about 6, and then optionally retaining the temperature for a period of
about 0.5 to about 6 hours; and

[0057](viii) cooling the reactor contents and isolating the particles, by
washing, and drying.

[0058]In another embodiment, a process for the preparation of toner
compositions comprises.

[0059](i) preparing an emulsion latex comprised of sodio sulfonated
polyester resin particles of from about 5 to about 500 nanometers in size
diameter by heating said resin in water at a temperature of from about
65° C. to about 90° C.

[0060](ii) preparing a pigment dispersion in water by dispersing in water
from about 10 to about 25 weight percent of sodio sulfonated polyester
and from about 1 to about 5 weight percent of pigment;

[0061](iii) adding the pigment dispersion to a latex mixture comprised of
sulfonated polyester resin particles in water with shearing, followed by
the addition of a divalent salt dissolved in water until aggregation
results as indicated by an increase in the latex viscosity of from about
2 centipoise to about 100 centipoise;

[0062](iv) heating the resulting mixture at a temperature of from about
45° C. to about 55° C. thereby causing further aggregation
and enabling coalescence, resulting in toner particles of from about 4 to
about 9icrons in volume average diameter and with a geometric
distribution of less than about 1.3; and optionally

[0063](v) cooling the product mixture to about 25° C. and followed
by washing and drying.

[0064]The present dry-powder electrophoretic displays comprise two sets of
oppositely charged toners. Namely, one set of toner particles is
negatively charged and the other set is positively charged. As used
herein, a set of toner particles refers to a plurality of toner particles
of the same color. A set of toner particles, has, in embodiments, the
same general composition and pigment/colorant makeup. As described
herein, the toner particles are generally emulsion/aggregation particles.
Emulsion/aggregation particles are typically negatively charged.
Therefore, at least one set of the toner particles needs to be treated to
impart a positive charge to the particles. Along these lines, a surface
coating is disposed on or applied to the surface of at least one set of
the toner particles, and in embodiments to the colored toner particles in
an electrophoretic display employing white toner particles and colored
toner particles. Generally, the surface coating should be optically
transparent, capable of forming a uniform film, and must also be a
non-conductive material. Materials suitable as the surface coating
include, but are not limited to, polycarbonate, and methacrylate
copolymers.

[0065]A suitable methacrylate copolymer is available from Rohm American
Inc. as EUDRAGIT®. The methacrylate copolymer is, in embodiments,
butylmethacrylate (2-dimethylaminoethyl)methacrylate-methylmethacrylate
copolymer (1:2:1). The methacrylate copolymer can be dispersed in water.
The copolymer possesses an average particle size diameter of for example,
from about 50 to about 500 nanometers (nm). In embodiments, the copolymer
possesses an average particle size of from about 100 to about 300
nanometers (nm).

[0066]Examples of specific polymers that may be selected are EUDRAGIT®
RL and RS polymers (Rohm Pharma) which are copolymers synthesized from
acrylic and methacrylic esters with a low content of quaternary ammonium
groups. EUDRAGIT® RL and RS differ in the molar ratios of the
ammonium groups to the remaining neutral (meth)acrylic acid esters (1:20
and 1:40 respectively). EUDRAGIT® NE polymers are an aqueous
dispersion of a neutral copolymer based on ethyl acrylate and methyl
methacrylate. EUDRAGIT® RD 100 is the powder form of copolymers of
acrylate and methacrylates with a quaternary ammonium group in
combination with sodium carboxymethylcellulose.

[0067]Various suitable effective amounts of the methacrylate copolymer
including, for example, the copolymer available from Rohm American Inc.
as EUDRAGIT®, can be selected. Generally, the surface coating
material should be present in an effective amount to provide a surface
coating that is from about 1 to about 10 percent by weight of the toner
composition. As used herein, the weight of the surface coating refers to
the percent by weight of the coating on each toner particle in the toner
composition. In embodiments, the surface coating material should be
present in an effective amount to provide a surface coating that is from
about 3 to about 7 percent by weight of the toner composition.

[0068]The surface coating may be disposed on or coated on the toner
particles by any suitable method. Suitable methods for forming surface
coated toners, and particularly toners coated with a methacrylate polymer
such as, for example, Eudragit® polymers, are described in U.S.
patent application Ser. No. 10/446,015 filed on May 27, 2003, the entire
disclosure of which is incorporated herein by reference. In embodiments,
the surface coating material is added in its dissolved form to an
acidified slurry of toner particles. The pH of the slurry is then
adjusted so that the surface coating material precipitates on the surface
of the toner. Without being bound to any particular theory, it is
believed that a film of the surface coating is formed on the surface of
the toner particles upon the evaporation of the water. By the formation
of the surface coating film the surface of the toner acquires the
(cationic) characteristics of the surface treatment additive, which
results in a positively charged toner.

[0069]In embodiments, the cationic polymer is a EUDRAGIT® series
polymer, such as, for example, EUDRAGIT® EPO (hereinafter "EEPO"),
which is reversibly soluble-insoluble in aqueous solution when the pH is
changed and, therefore, the solubility of EEPO can be considered
pH-dependent. The EEPO becomes water soluble via salt formation with
acids and can be added in this form to the acidic toner slurry. It is
hypothesized that the water-soluble polymer would interact in solution
with the toner particles even at low pH. Once the polymer has time to
adsorb to the toner particles, the pH can be shifted to basic conditions.
At this point the polymer will precipitate onto the toner's surface and
form a film around the toner upon the evaporation of water. The surface
of the toner is hypothesized to acquire the cationic characteristics of
the polymer resulting in a positive charged toner.

[0070]More specifically, in embodiments, the EEPO polymer contains
tertiary amino functional groups capable of ionic interactions with, for
example, sulfonated groups on the surface of the polyester toner. The
neighboring polymer chain and toner particle surface become complexed to
one another resulting, in a modification of the properties of the
particle surface and thus the tribocharging characteristics. The surface
treatment approach, in embodiments, is to add the polymer in its
dissolved form to the toner slurry following the toner fabrication
process. The toner slurry is adjusted to a pH of for example from about 2
to about 3 to permit the EEPO to remain dissolved during the addition
period. It is hypothesized that the water-soluble polymer interacts with
the toner particles via electrostatic attraction, even at low pH, and
will not substantially precipitate or irreversibly complex to each other.
Once the pH is increased to from about 10 to about 12, the EEPO will
precipitate onto the toner surface and form a film or layer of
positive-charged polymeric material around the toner surface. Evaporating
the water from the toner by for example, freeze drying the toner
particles promotes further coalescence of the polymeric film to the toner
surface.

Schematic Illustrative Representation of EEPO Layering or Precipitation on
the Toner Particle Surface.

##STR00002##

[0072]In embodiments employing a set of white toner particles and a set of
colored or black toner particles, the white toner particles typically
carry a negative charge, and the colored or black toner particles
typically include a surface coating as described herein. In embodiments
employing two different colored toners, any toner may be the negatively
charged toner and any toner may be treated with a surface coating as
described herein.

[0073]In embodiments, the toner particles have a particle size of less
than about 20 micrometers. In other embodiments, the toner particles have
a particle size of from about 1 to about 20 micrometers. In further
embodiments, the toner particles have a particle size of about 1 to about
10, and may be from about 4 to about 7 micrometers.

[0074]In another preferred embodiment, the toner particles comprises a
shape factor of about 110 to about 130, where a shape factor of 100 is
defined as a particle which is perfectly spherical in shape. The present
application would require that the particle be as spherical in shape to
reduce the drag, and hence provide easier movement on applying an
electrical field. In another preferred embodiment, the toner particles
comprises of a particle circularity of about 0.920 to about 0.980, as
measured by the FPIA instrument, where a particle circularity of 1.00 is
considered perfectly spherical.

[0075]The present toner particles may be used in a dry-powder
electrophoretic display. A dry-powder electrophoretic display, as used
herein contains either no dispersion fluid or is substantially free of a
dispersion fluid. Modifying the surface of the toners, such as with a
surface coating as described herein, allows for selective tuning of the
surface charge to be either positive or negative.

[0076]Two sets of oppositely charged dry toner particles are disposed
between two electrodes. The electrodes are separated by spacer beads
which create an air gap between the two electrodes. Generally, at least
one of the two sets of toner particles includes a surface coating as
described herein to impart a positive charge to the set of toner
particles. As the charge on the electrodes is reversed, the oppositely
charged toner particles migrate back and forth across the gap in response
to the electric field, thereby creating a light or dark image to the
viewer.

[0077]Typically, to create an image, the electrodes or substrates are
connected to a voltage source. As the charge or an electrode is changed,
the charged particles migrate toward the oppositely charged electrode.
When a negative voltage is applied to the upper electrode or conductive
substrate, the positively charged toner particles comprising the surface
coating migrate to the upper electrode as conductive substrate to give an
appearance corresponding to the color of the positively charged toner
particles. When a positive charge is applied, the negatively charged
toner particles, i.e., the toner particles without the surface coating,
migrate toward the upper electrode or conductive substrate to provide a
color appearance corresponding to the color of the negatively charged
toner particles. The color appearance will remain in a given state even
if a voltage is not applied.

[0078]The present exemplary embodiments are further illustrated by the
following examples. The examples are merely illustrative, and are not
intended to be limiting in any manner.

EXAMPLES

Example I

Surface Treated Toners

Preparation of Sodio Sulfonated Polyesters:

[0079]A linear sulfonated random copolyester resin comprised of, on a mol
percent basis, 0.465 of terephthalate, 0.035 of sodium sulfoisophthalate,
0.475 of 1,2-propanediol, and 0.025 of diethylene glycol was prepared as
follows. In a 5 gallon Parr reactor equipped with a bottom drain valve,
double turbine agitator, and distillation receiver with a cold water
condenser were charged 3.98 kilograms of dimethylterephthalate, 451 grams
of sodium dimethyl sulfoisophthalate, 3.104 kilograms of 1,2-propanediol
(1 mole excess of glycol), 351 grams of diethylene glycol (1 mole excess
of glycol), and 8 grams of butyltin hydroxide oxide catalyst. The reactor
was then heated to 165° C. with stirring for 3 hours whereby 1.33
kilograms of distillate was collected in the distillation receiver, and
which distillate was comprised of about 98 percent by volume of methanol
and 2 percent by volume of 1,2-propanediol as measured by the ABBE
refractometer available from American Optical Corporation. The reactor
mixture was then heated to 190° C. over a one hour period, after
which the pressure was slowly reduced from atmospheric pressure to about
260 Torr over a one hour period, and then reduced to 5 Torr over a two
hour period with the collection of approximately 470 grams of distillate
in the distillation receiver, and which distillate was comprised of
approximately 97 percent by volume of 1,2-propanediol and 3 percent by
volume of methanol as measured by the ABBE refractometer. The pressure
was then further reduced to about 1 Torr over a 30 minute period whereby
an additional 530 grams of 1,2-propanediol were collected. The reactor
was then purged with nitrogen to atmospheric pressure, and the polymer
product discharged through the bottom drain onto a container cooled with
dry ice to yield 5.60 kilograms of 3.5 mol percent sulfonated polyester
resin, sodio salt of
(1,2-propylene-dipropylene-5-sulfoisophthalate)-copoly(1,2-propylene-dipr-
opylene terephthalate). The sulfonated polyester resin glass transition
temperature was measured to be 56.6° C. (onset) utilizing the 910
Differential Scanning Calorimeter available from E.I. DuPont operating at
a heating rate of 10° C. per minute. The number average molecular
weight was measured to be 3,250 grams per mole, and the weight average
molecular weight was measured to be 5,290 grams per mole using
tetrahydrofuran as the solvent.

Preparation of a Sodio Sulfonated Polyester Colloid Solution:

[0080]A 15 percent solids concentration of a colloidal solution of
sodio-sulfonated polyester resin particles with particle diameter sizes
of from about 5 to about 150 nanometers, and typically about 20 to about
40 nanometers dissipated in 85 percent aqueous media of water was
prepared by first heating about 2 liters of deionized water to about
85° C. with stirring, and adding thereto 300 grams of the above
prepared sulfonated polyester resin, followed by continued heating at
about 85° C., and stirring of the mixture for a duration of from
about one to about two hours, followed by cooling to about room
temperature, about 25° C. throughout the Examples. The colloidal
solution of sodio-sulfonated polyester resin particles possessed a
characteristic blue tinge and particle sizes of from about 5 to about 150
nanometers, and typically of about 20 to about 40 nanometers, as measured
by the NiCOMP® particle sizer.

Toner 1: Sodio Sulfonated Polyester Toner (Control, Untreated)

[0081]A pilot plant batch of toner comprised of a sodio-sulfonated
polyester (SPE4, 12% solids and 88% deionized water), 9% Carnauba wax
dispersion and 6%-wt of Flexiverse Blue (Pigment Blue 15:3, BFD1121,
47.1% solids) dispersion (Sun Chemical Co.) was prepared. Aggregation of
the cyan polyester toner particles was completed at 58° C.
(degrees Centigrade throughout) in a 30-gallon stainless steel reactor
(of which only 20 kg of the toner yield was used for bench scale
studies). The agitation rate was set initially to 100 RPM. A 5% zinc
acetate solution was added as the coagulant via the FIZA or fast initial
zinc addition (FIZA) technique as illustrated in U.S. Pat. No. 6,395,445,
where 60-80% of the total zinc acetate solution was added quickly (600
g/min for the first 30 minutes) and the remainder (80-100 g/min
thereafter) was added at a reduced rate. The amount of zinc acetate added
equaled approximately 11% of the total resin in the emulsion. After 7
hours of aggregation, the particle size reached 5.24 μm with a GSD of
1.2. Full cooling was applied and particles were sieved at 30-35°
C. through a 25 μm nylon filter bag. A portion of the toner slurry was
washed in the lab three times with deionized water after the mother
liquor removal, resuspended to approximately 25% weight solids and
freeze-dried for 48 hours to provide the untreated parent toner (VF173 or
Control). This toner was comprised of 85% sodio-sulfonated polyester, 9%
Carnauba wax dispersion and 6%-wt of Flexiverse Blue pigment.

Toner 2: Treated Sodio Sulfonated Polyester Toner

Preparation of EEPO Solution

[0082]An aminoalkylmethacrylate copolymer called Eudragit EPO (EEPO),
which was delivered to toner as a 1 percent (wt/wt) solution in deionized
water (DIW), was prepared by dissolving 1.26 grams of the EEPO in 124.7
grams of 0.3 M HNO3; the pH of the solution was lowered to 2.0 by
adding 2.4 grams of 1.0 M HNO3. Lowering the pH of the aqueous
solution to 2.0 ensured complete solubility of the EEPO polymer in the
solution. The total percentage of EEPO to toner was to equal 3% weight of
dry toner.

Coating Procedure of EEPO onto Surface of Polyester Toner Particles

[0083]The above toner (Toner 1) made up of 85% sodio-sulfonated polyester,
9% Carnauba wax dispersion and 6%-wt of Flexiverse Blue was treated in
the lab via a pH shifting procedure where EEPO is soluble or insoluble in
an aqueous solution depending on the pH of the aqueous solution.

[0084]A 327 gram quantity of the toner slurry (12.9%-weight solids in
87.1% mother liquor) made up of 85% sodio-sulfonated polyester, 9%
Carnauba wax dispersion and 6%-wt of Flexiverse Blue pigment was
separated from its mother liquor via decanting, and then stirred in a 1-L
glass Erlenmeyer flask on a stir plate at 250-300 rpm. The pH of the
toner slurry was lowered from 5.5 to 2.4 by the addition of 70 grams of
0.3 M HNO3. The EEPO solution was added drop wise to the toner
slurry and stirred for 1 hour at room temperature. After 1 hour the pH of
the toner slurry was increased to 12.2 with 71 grams of 1.0 M NaOH and
left to stir at 300 rpm for 18 to 20 hours overnight at ambient
temperature. The surface-treated toner was then filtered and washed four
times. The filtercake was then resuspended to approximately 25%-wt solids
and freeze-dried. The pH of the filtrates was always greater than 9.5 and
showed no sign of precipitated EEPQ; it can be assumed that all EEPO
polymer was transferred to the toner surface. This toner was comprised
of--85% sodio-sulfonated polyester, 9% Carnauba wax dispersion and 6%-wt
of Flexiverse Blue pigment with 3% EEPO relative to dry toner weight
deposited or coated on the toner's surface.

Example II

Untreated Toners

Preparation of Styrene Butylacrylate Carboxylic Acid Latex: (Latex B)

[0085]A latex emulsion (i) comprised of polymer particles generated from
the emulsion polymerization of styrene, butyl acrylate and beta carboxy
ethyl acrylate (Beta CEA) was prepared as follows. A surfactant solution
of 434 grams of DOWFAX 2A1®--disodium dodecyl diphenyloxide
disulfonate (anionic emulsifier) and 387 kilograms of deionized water was
prepared by mixing for 10 minutes in a stainless steel holding tank. The
holding tank was then purged with nitrogen for 5 minutes before
transferring the mixture into a reactor. The reactor was then
continuously purged with nitrogen while being stirred at 100 RPM. The
reactor was then heated to 80° C.

[0086]Separately, 6.11 kilograms of ammonium persulfate initiator were
dissolved in 30.2 kilograms of deionized water. Also, separately a
monomer emulsion A was prepared in the following manner. 315.7 Kilograms
of styrene, 91.66 kilograms of butyl acrylate, 12.21 kilograms of
beta-CEA, 7.13 kilograms of 1-dodecanethiol, 1.42 kilograms of decanediol
diacrylate (ADOD), 8.24 kilograms of DOWFAX® (anionic surfactant), and
193 kilograms of deionized water were mixed to form an emulsion. Five
percent of the above emulsion was then slowly fed into the reactor
containing the aqueous surfactant phase at 80° C. to form the
seeds wherein the "seeds" refer, for example, to the initial emulsion
latex added to the reactor, prior to the addition of the initiator
solution, while being purged with nitrogen. The above initiator solution
was then slowly charged into the reactor, forming about 5 to about 12
nanometers of latex "seed" particles. After 10 minutes, the remainder of
the emulsion was continuously fed in using metering pumps.

[0087]Once all of the above monomer emulsion was charged into the main
reactor, the temperature was maintained at 80° C. for an
additional 2 hours to complete the reaction. The reactor contents were
then cooled down to about 25° C. The resulting isolated product
was comprised of 40 weight percent of submicron, 0.5 micron, diameter
resin particles of styrene/butylacrylate/beta CEA suspended in 60 percent
water and 1.5 pph of the anionic surfactant. The molecular properties
resulting for the resin latex were Mw of 39,000, Mn of 10.8, as
measured by a Gel Permeation Chromatograph, and a midpoint Tg of
55.8° C., as measured by a Differential Scanning Calorimeter,
where the midpoint Tg is the halfway point between the onset and the
offset Tg of the polymer.

Preparation of Cross-Linked Latex (Latex C)

[0088]A cross-linked latex emulsion comprised of polymer particles
generated from the emulsion polymerization of styrene, butyl acrylate and
beta carboxy ethyl acrylate (β) CEA was prepared as follows. A
surfactant solution of 4.08 kilograms of NEOGEN® RK (anionic
emulsifier) and 78.73 kilograms f deionized water was prepared by mixing
these components for 10 minutes in a stainless steel holding tank. The
holding tank was then purged with nitrogen for 5 minutes before
transferring the resulting mixture into the above reactor. The reactor
was then continuously purged with nitrogen while the contents were being
stirred at 100 RPM. The reactor was then heated up to 76° C., and
held there for a period of 1 hour.

[0090]Also separately, monomer emulsion was prepared in the following
manner. 47.39 Kilograms of styrene, 25.52 kilograms of butyl acrylate,
2.19 kilograms of β-CEA, 0.729 kilogram of divinyl benzene (DVB)
crosslinking agent, 1.75 kilograms of NEOGEN® RK (anionic surfactant),
and 145.8 kilograms of deionized water were mixed to form an emulsion.
One (1) percent of the emulsion was then slowly fed into the reactor,
while the reactor was being purged with nitrogen, containing the aqueous
surfactant phase at 76° C. to form "seeds". The initiator solution
was then slowly charged into the reactor and after 40 minutes the
remainder of the emulsion was continuously fed in using metering pumps
over a period of 3 hours.

[0091]Once all the monomer emulsion was charged into the above main
reactor, the temperature was held at 76° C. for an additional 4
hours to complete the reaction. Cooling was then accomplished and the
reactor temperature was reduced to 35° C. The product was
collected into a holding tank. After drying, the resin latex onset Tg was
53.5° C. The resulting latex was comprised of 25 percent
cross-linked resin, 72.5 percent water and 2.5 percent anionic
surfactant. The resin had a ratio of 65:35:3 pph:1 pph of styrene:butyl
acrylate:β-CEA:DVB. The mean particle size of the gel latex was 50
nanometers as measured on disc centrifuge, and the resin in the latex
possessed a crosslinking value of 25 percent as measured by gravimetric
method.

Toner 3: White Particles (Non Cross-Linked)

[0092]310 grams of the above prepared latex emulsion (latex B) and 164
grams of an aqueous titanium dioxide (TiO2) dispersion containing 97
grams of TiO2 with a solids loading of 66.6 percent, were
simultaneously added to 600 milliliters of water with high shear stirring
by means of a polytron. To this mixture was added 11.25 grams of a
polyaluminum sulfosilicate (PASS) solution containing 1.25 grams of PASS,
10 percent solids and 10 grams of 0.2 molar nitric acid, over a period of
1 minute, followed by the addition of 11.25 grams of cationic surfactant
solution containing 1.25 grams of the coagulant SANIZOL B® (60 percent
active ingredients) and 10 grams of deionized water, and blended at a
speed of 5,000 rpm for a period of 3 minutes. The resulting mixture was
transferred to a 2 liter reaction vessel and heated at a temperature of
47° C. for 120 minutes resulting in aggregates of a size of 6
micrometers and a Geometric Standard Deviation ("GSD") of 1.19. To the
toner aggregates were added 130 grams of the above prepared latex
followed by stirring for an additional 90 minutes; the temperature was
held at 47° C. The particle size of the aggregates was found to be
6.2 with a GSD of 1.19.

[0093]The pH of the resulting mixture was then adjusted from 2 to 7.9 with
aqueous base solution of 4 percent sodium hydroxide and allowed to stir
for an additional 15 minutes. Subsequently, the resulting mixture was
heated to 93° C. and retained there for a period of 1 hour where
the particle size measured was 6.2 micrometers with a GSD of 1.20. This
was followed by the reduction of the pH to 5.8 with 4 percent nitric acid
solution and allowed to stir for an additional 40 minutes. The particle
size was 6.2 micrometers with a GSD of 1.20. The pH of the mixture was
further decreased to 5, and allowed to coalesce for an additional 1 hour
resulting in spherical particles with a size of 6.3 micrometers and a GSD
of 1.21. The reactor was then cooled down to room temperature and the
particles were washed 4 times with deionized water. The toner particles
obtained were comprised of 73 percent styrene butylacrylate BCEA resin
and 27 percent titanium pigment, and these particles dried on a freeze
dryer at a temperature of -80° C. for a period of 2 days.

Toner 4: White Particle (Cross-Linked)

[0094]About 222 grams of the above prepared latex emulsion (latex B) along
with 88 gm of latex C and 164 grams of an aqueous titanium dioxide
(TiO2) dispersion containing 64 grams of TiO2 with a solids
loading of 66.6 percent, and 33.4 percent water were simultaneously added
to 600 milliliters of water with high shear stirring by means of a
polytron. To this mixture were added 11.25 grams of a polyaluminum
sulfosiliate (PASS) solution containing 1.25 grams of PASS of 10 percent
solids of polyaluminum sulfosilicate and 10 grams of 0.2 molar nitric
acid, over a period of 1 minute, followed by the addition of 11.25 grams
of a cationic surfactant solution containing 1.25 grams of the coagulant
SANIZOL B® (60 percent active ingredients) and 10 grams of deionized
water and blended at a speed of 5,000 rpm for a period of 3 minutes. The
resulting mixture was transferred to a 2 liter reaction vessel and heated
at a temperature of 45° C. for 110 minutes resulting in aggregates
of a size diameter of 5.1 micrometers and a Geometric Standard Deviation
("GSD") of 1.20. To the resulting toner aggregates were added 130 grams
of the above prepared latex followed by stirring for an additional 90
minutes; the temperature was then increased to 47° C. The particle
diameter size of the aggregates was found to be 5.4 and a GSD of 1.19.

[0095]The pH of the resulting mixture was then adjusted from about 2 to
about 7.9 with aqueous base solution of 4 percent sodium hydroxide and
allowed to stir for an additional 15 minutes. Subsequently, the resulting
mixture was heated to 93° C. and retained there for a period of 1
hour where the particle size of the formed aggregates was 5.6 micrometers
with a GSD of 1.21. This was followed by the reduction of the pH to 5.5
with 5 percent nitric acid solution and followed by stirring for an
additional 40 minutes. The diameter particle size of the formed
aggregates measured was 5.7 micrometers with a GSD of 1.21. The pH of the
mixture was further decreased to 5 and allowed to coalesce for an
additional 1 hour, resulting in spherical particles with a size diameter
of 5.7 micrometers and a GSD of 1.21. The reactor was then cooled down to
room temperature, about 22° C. to about 25° C., and the
resulting particles were washed 4 times with deionized water with the
final wash at a pH of 4. The particles were then dried on a freeze dryer
at a temperature of -80° C. for a period of 2 days. The toner
particles obtained were comprised of 60 percent styrene butylacrylate
BCEA, 20 percent styrene butylacrylate BCEA, bivinylbenzene resin and 20
percent titanium dioxide pigment.

[0100]The above toners were identified as candidate materials for
dry-powder electrophoretics. The following toner combinations were tested
in a parallel plate cell as follows. A small quantity of positive and
negatively charged toner particles (around 10-20 mg each) were added to a
glass vial, followed by 5-10 mg of 25 um glass fiber spacer particles.
The toner and fiber mixture was thoroughly mixed with a small spatula,
and the mixture was applied to a 2×2 inch ITO coated glass plate by
tapping. The powder was spread by hand to create a uniform coating on the
ITO coated glass surface. The coated glass plate was covered with a
second glass plate and the two plates were rubbed back and forth against
one another to further spread the toner mixture, and evenly distribute
the spacer fibers. The two plates were finally secured together using
binder clips.

[0101]The above toner combinations showed good color coverage when the
voltage of the cell is switched. A square waveform voltage of +/-200V
with frequency of 300 mHz was applied across the two ITO coated glass
plates, and a distinct contrast was observed as the toner particles
migrated back and forth across the cell gap.

Example 3

[0102]A dry-powder cell was prepared with ITO glass electrodes coated with
silicone sealant spray. White toner particles (Toner 3) and black toner
particles (Toner 7) were used in the cell. A voltage of about 80 to about
90 volts was applied across the cell, and an AC field overlay of 80 volts
with a frequency of 300 Hertz was applied simultaneously. The cell shows
good coverage of the black and white colors as the voltage is switched.

[0103]The use of emulsion aggregation particles in an electrophoretic
display including emulsion aggregation particles with a surface coating
to impart a positive charge to select particles as described herein
provides a satisfactory dry-powder electrophoretic display. Improved
device performance is realized in that the highly cross-linked toner
particles are more resistant to melting and agglomeration as compared to
conventional "inks." Additionally, modifying the surface of some toner
particles with a surface coating, as described herein, allows for
selective tuning of the surface charge to be positive or negative.

[0104]While particular embodiments have been described, alternatives,
modifications, variations, improvements, and substantial equivalents that
are or may be presently unforeseen may arise to applicants or others
skilled in the art. Accordingly, the appended claims as filed and as they
may be amended are intended to embrace all such alternatives,
modifications variations, improvements, and substantial equivalents.

Patent applications by Jurgen Daniel, Mountain View, CA US

Patent applications by Man-Chung Tam, Mississauga CA

Patent applications by Meng H. Lean, Santa Clara, CA US

Patent applications by Naveen Chopra, Oakville CA

Patent applications by Raj D. Patel, Oakville CA

Patent applications by Valerie M. Farrugia, Oakville CA

Patent applications by Palo Alto Research Center Incorporated

Patent applications in class Changing position or orientation of suspended particles

Patent applications in all subclasses Changing position or orientation of suspended particles